Safety evaluation using behavioral simulation models

This paper describes a design environment called ADEPT (advanced design environment prototype tool) which enables designers to assess the dependability of systems early in the design process using behavioral simulation models. ADEPT is an interactive graphical design environment which allows design and analysis of systems throughout the entire design cycle. ADEPT supports functional verification, performance evaluation, and dependability analysis early in the design cycle from a single model in order to dramatically reduce design cycles and deliver products on schedule. In this paper, ADEPT is applied to the design of a distributed computer system used to control trains. Two distinct experiments were run to illustrate dependability evaluation using behavioral simulation models. The first experiment evaluates the effectiveness of using a simple (7,4) Hamming code for protecting information in a distributed system. The second experiment evaluates the effectiveness of a watchdog monitor whose role is to detect hardware and software errors in the distributed system. The experiments illustrate dependability analysis using behavioral simulation models. The first simulation demonstrates estimation of the error coverage of the (7,4) code and the mean time to hazardous event (MTTHE). The second experiment demonstrates functional verification and controllability of behavioral simulation experiments by testing the response of a watchdog monitor design to rare malicious events.